美国西部的地震活动区由于缺少150年前地震的文字记载,大地震的频度只能依据地质证据来推测。在犹他州盐湖城附近,沿瓦沙特卡断层分布的陡崖反映这一事实:距今12,000年前邦维尔湖后退后形成的冲积层的累计地表位移达10米。Swan等人最近进行的槽探研究表明,所发现的古代地表土层的间断,反映了当时一系列重大的地表断裂事件,对这些沉积 Seismic Areas in the Western United States Due to the lack of written records of earthquakes 150 years ago, the frequency of major earthquakes can only be inferred based on geological evidence. Near Salt Lake City, Utah, the steep cliffs along the Wakatka fault reflect the cumulative surface displacement of alluvial formations that formed 12,000 years ago after the Lake Bonville retreated to 10 meters. Swan et al. Conducted a recent trench probing study showing that the discontinuities in the ancient surface soils revealed a series of major surface ruptures at that time,